This is a hard one to explain because we need to understand several different
things about English grammar in order to be able to choose the right answer.
In a nutshell, we need a preposition
here between the with the head
noun and the sentencethe surface of metal is first covered with an acid and then inscribed with
some sharp instrument.

In other words, the sentence that comes from the adjective
clause would look like this:

The surface of metal is first covered with an acid and then inscribed with
some sharp instrument in [this] process.

TestMagic has two helpful strategies related to this question. Click below to
read them: